The primary difference between ice pellets (sleet) and hail lies in their formation process, size, and appearance. Ice pellets are small, hard spheres of ice that form when snowflakes partially or completely melt while falling through a layer of warm air, then refreeze in a subsequent layer of cold air. Hail, on the other hand, consists of layers of ice that accumulate as an ice nucleus is repeatedly lifted into and falls through thunderstorms, collecting supercooled water that freezes onto it.
Here's a breakdown of the key distinctions:
Formation:
- Ice Pellets (Sleet): Form when snowflakes melt and then refreeze before reaching the ground. The melting occurs in a warm air layer aloft, and the refreezing occurs in a shallow layer of cold air near the surface.
- Hail: Forms within thunderstorms where strong updrafts repeatedly lift ice particles into regions of supercooled water. This water freezes onto the particle, adding layers of ice until the hailstone becomes too heavy and falls to the ground.
Size:
- Ice Pellets (Sleet): Typically small, usually 5 mm (0.2 inches) in diameter or less.
- Hail: Can range in size from 5 mm (0.2 inches) to larger than a softball (over 10 cm or 4 inches in diameter).
Appearance:
- Ice Pellets (Sleet): Appear as small, translucent or clear, hard ice spheres. They often bounce when hitting the ground.
- Hail: Can be opaque or have alternating layers of clear and opaque ice. Large hailstones may have irregular shapes.
Summary Table:
| Feature | Ice Pellets (Sleet) | Hail |
|---|---|---|
| Formation | Melting and refreezing of snowflakes. | Accretion of supercooled water in thunderstorms. |
| Size | Small (≤ 5 mm) | Variable (5 mm to > 10 cm) |
| Appearance | Small, round, translucent or clear ice spheres. | Can be opaque or layered, often larger and more irregular in shape. |
In essence, ice pellets are essentially refrozen raindrops, while hail is a product of complex thunderstorm dynamics involving repeated cycles of freezing and accretion.
